Two that I have done had pretty much the same symptoms, and a complete head rebuild fixed the smoke. The rings and cylinders seem quite durable.

An easy way to tell is to run a compression test, then put a teaspoon of oil in each cylinder and re-test. If your "wet" reading is 30% more than the "dry", then you have ring/cylinder problems.

These engines are prone to oil leaks around the cam box - head seal, and at the front crank seal, and the carbs can have problems.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe